Phase Modulated Fiber Optic Link with Up to 20 Gigahertz Bandwidth and 40dB Dynamic Range

OPTRA has identified an approach for using Integrated Phase Modulators (IPM) to optically measure voltages in an anechoic chamber which is unique, innovative and superior to any other method currently in use. We propose the use of an IPM to phase shift the two propagation eigen-modes of a highly birefringent optical fiber and to directly recover this phase, which is proporational to the voltage being measured, using a method which is independent of the operating point of the system. This system is independent of the operating point of the system. This system will use a continuous wave (CW) fiber coupled diode pumped solid state laser source to achieve high signal to noise ratio shot noise limited performance. OPTRA's method of phase detection removes the +-1/8 cycle (45 degrees) maximum phase excursion which is typical of Mach-Zehnder amplitude modulators and extends the dynamic range to cover the full potential of the IPM device. This translates to a factor of 40 increase in dynamic range for commonly available IMP devices. The maximum modulation rate for OPTRA's approach is limited only by the IPM and not by laser chirp or nonlinear amplifier effects as in direct amplitude modulation. The maximum modulation rates reported using Lithium Niobate waveguide based IPM are aound 20GHz.